Cells of all organisms produce products that are secreted into their surroundings to form an extracellular matrix (ECM). In multicellular organisms the interactions between the ECM and the intracellular compartment play an important role in controlling many developmental decisions. It is well established that in animal cells the ECM molecules are constituents of selective cell-cell recognition and celI-ECM adhesion process and important in regulation of cellular polarity, differentiation, cell division, cell death and cell migration. This proposal concerns a family of ECM-associated cell surface receptor protein kinases called WAKs (Wall Associated Kinases) that are discovered in the cells of the model flowering plant, Arabidopsis. WAKs contain EGF (epidermal growth factor)-Iike domains and represent a unique class of receptor like kinases (RLK) in higher plants. WAKs are the best candidates for adhesion receptors that exchange signals between the extracellular and intracellular compartments. More than 26 WAK or WAK-like kinase (WLK) genes have been identified in the genome of Arabidopsis. Many of the WAK/WLK gene members exist as tight gene clusters and can be classified as PR (pathogen-related) genes. Molecular and genetic analyses have suggested that, while some WAK members are involved in pathogenesis, others are required for cell elongation and plant development. This proposal describes experiments to dissect the signaling pathways associated with WAK/WLK members and to determine the role WAKs/WLKs have in signal transduction between the plant ECM and the cytoplasm. The analysis of the WAK/WLK family of proteins may lead to a new signal transduction mechanism in plant cells, and perhaps towards general principals of how eukaryotic cells perceive signals in their ECM and environment.